Boron nitride base evaporation vessel having a surface coating of titanium-silicon thereon

ABSTRACT

A boron nitride containing evaporation vessel which is readily wetted by molten metals and accordingly ideally suited for use in a vacuum metallizing system is provided by coating at least a portion of the evaporation surface of the vessel with a titaniumsilicon base alloy.

United States Patent [191 Montgomery [451 May 1, 1973 1 1 BORON NITRIDEBASE EVAPORATION VESSEL HAVING A SURFACE COATING OF TITANIUM-SILICONTHEREON [75] Inventor: Lionel C. Montgomery, North Olmsted, Ohio [73]Assignee: Union Carbide Corporation, New

York, N.Y.

[22] Filed: Jan. 18, 1971 21 Appl,No.: 107,542

Related US. Application Data [63] Continuation of Ser. No. 742,446, July3, 1968,

abandoned,

[52] US. Cl. ..266/39, 117/123 B, 263/48 [51] Int. Cl ..C23c 13/12 [58]Field of Search ..266/39, 43; 263/47, 263/48; 117/123 A, 123 B [56]References Cited UNlTED STATES PATENTS 3,031,340 4/1962 Girardot ..117/123 B X 3,063,865 1 H1962 Baer et a1. ..266/39 X 3,084,060 4/1963Baer et al. ..266/43 X 3,181,968 5/1965 Mandorf, .lr ..266/39 X3,216,710 ll/l965 Lenihan, Jr. et 81.... ..263/48 3,227,431 l/ 1966Steeves ..263/48 3,245,674 4/1966 Baer et a1. ..266/39 OTHERPUBLICATIONS Boron Nitride Technical Data, Carborundum Latrobe Plant,42766 pp. l-5.

Primary Examiner-R. Spencer Annear Attorney.lames C. Arvantes et a1.

[57] ABSTRACT A boron nitride containing evaporation vessel which isreadily wetted by molten metals and accordingly ideally suited for usein a vacuum metallizing system is provided by coating at least a portionof the evaporation surface of the vessel with a titanium-silicon basealloy.

10 Claims, 1 Drawing Figure PATENTEDHAY Hm 3730,50?

INVENTOR LIONEL C MON'IAGOMERY ATTORNEY BACKGROUND OF THE INVENTION 1.Field of the Invention The present invention relates to a refractoryboron l0 nitride containing evaporation vessel having deposited on itsevaporation surface a titanium-silicon base coating which is readilywetted by molten metals, such as molten aluminum and the like, with thecoating having been formed thereon by reacting a portion of thetitanium-silicon base alloy with the contacted boron nitride portion ofthe vessel at elevated temperatures.

2. Description of the Prior Art It is common practice to metallize orcoat various articles fashioned from such diverse materials as steel,rubber, plastic and the like by vapor depositing aluminum thereon.

In practice, the actual coating or metallizing of an article is carriedout in a vacuum chamber which contains both the metal to be vaporizedand, in a spaced apart relationship, the article to be coated ormetallized. Generally, the metal to be vaporized is held or placed in arefractory vessel or crucible and heated therein to a temperaturesufficient to cause it to become molten and commence to vaporize.

In the foregoing general process it is essential that a vessel orcrucible be employed which does not react substantially with the moltenaluminum. This requirement is exceptionally well satisfied by fashioningsuch a vessel or crucible from a refractory material such as boronnitride or a boron nitride base composite. However, one difficulty whichis experienced with the use of this type of material is slow or limitedwetting of the boron nitride base evaporation vessel by molten aluminumduring the start up of the metallizing apparatus. This delay in wettingreduces the total efficiency of the metallizing process and is to beavoided, if possible.

The present invention overcomes the foregoing problems by providing acoating which when applied to a boron nitride base vessel renders itreadily wetted by molten metals, such as molten aluminum and the like.

SUMMARY Briefly, the instant invention is accomplished by coating atleast a portion of the evaporation surfaceof a boron nitride basecrucible or vessel which is intended for use in a vacuum metallizingsystem with a titanium-silicon base alloy which is both chemically andmechanically bonded thereto.

The titanium-silicon alloy is bonded to the evaporation surface of thecrucible or vessel by coating that portion of the body desired to betreated with a titanium-silicon base alloy and then heating the coatedbody to a temperature sufficient to cause a portion of thetitanium-silicon alloy to diffuse into the boron nitride base body andreact with the contacted boron nitride therein while leaving at least amolecular layer of undiffused titanium-silicon alloy on the surface ofthe body.

The resultant titanium-silicon alloy coated boron nitride baseevaporation vessel or crucible is ideally suited for use as a containerfor molten aluminum in a conventional vacuum metallizing system.

Accordingly, it is the principal object of the instant invention toprovide a boron nitride base vessel which has on at least one of itssurfaces a titanium-silicon coating which is readily wetted by moltenaluminum and the like.

Another object of the invention is to provide a boron nitride basecrucible or vessel which is suited for use in a conventional vacuummetallizing system.

DESCRIPTION OF THE DRAWING The sole FIGURE shown in the drawingpresented herewith is an isometric illustration of a rectangular vesselor crucible of the type commonly employed in a conventional vacuummetallizing apparatus.

Referring now to the drawing in detail, there is shown an isometricillustration of an evaporation vessel 1 having a cavity thereindesignated by the numeral 2. The floor of the cavity 2 constitutes theevaporation surface of the vessel l and is coated with atitanium-silicon base alloy 4 which is chemically and mechanicallybonded thereto. The evaporation vessel 1 is formed of a boron nitridebase refractory material 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION The evaporationvessel may be fabricated either from commercially pure boron nitride orfrom a refractory composite material which contains a substantial amountof boron nitride. In practice, it is preferred to employ a refractorycomposite which contains at least 20 weight per cent boron nitride. Goodresults have been obtained by employing a vessel containing all boronnitride or one containing from about 20 to about weight per cent boronnitride with the remainder being a compatable refractory material suchas titanium diboride. The titanium diboride is added to the boronnitride base material to render the resultant article electricallyconductive, if such is desired. However, it should be noted thatrefractory materials other than titanium diboride may be employed in thepractice of the instant invention. For example, the boron nitridecontaining vessel may also contain one or more other refractorymaterials such as zirconium diboride, aluminum nitride, titaniumnitride, calcium fluoride and the like. The foregoing list of materialsis illustrative only and is not intended to unduly limit the scope ofthe instant invention.

Generally, the titanium-silicon alloy is bonded to the evaporationsurface of the boron nitride containing vessel by coating it either witha molten titanium-silicon alloy, such as by flame spraying, or a slurryof titanium-silicon particles and then heating the socoated body to atemperature sufficient to cause some of the alloy to diffuse into theboron nitride containing body and react with the contacted boron nitridewhile leaving at least a molecular layer of titanium-silicon alloy onthe surface of the body. When the slurry technique is employed, thecoating of titanium-silicon particles should not be heated above themelting point of the alloy, the preferred temperature range being fromabout 1,400 C. to about l,500 (1., depending on the exact alloycomposition employed. Methods for forming a slurry of titanium-siliconparticles are well known in the art and they will not be discussed indetail herein.

It should be noted here that the main advantage afforded by thebeforementioned slurry technique is that it enables one to more easilycoat irregularly shaped boron nitride containing bodies. In addition, itshould also be noted that best results are obtained when thetitanium-silicon alloy employed contains from about 40 to about 80weight per cent silicon with the remainder being essentially titanium.This compositional range is preferred regardless of the method used toapply the alloy to the boron nitride containing vessel or crucible.

The following example illustrate in detail the practice of the instantinvention.

EXAMPLE A rectangular vessel of the type shown in the drawing 6% incheslong by 1% inches in width by one-half inch in height having a cavitytherein of approximately 3 cubic inches was fashioned from a compositerefractory material comprising 50 weight per cent boron nitride with theremainder being essentially titanium diboride.

A slurry of titanium silicide particles having an average particle sizeof between 2 and 5 microns was prepared by suspending a powdered 44weight per cent titanium, 56 weight per cent silicon alloy in a xyleneslip which contained volume per cent cyclopentadiene as a deflocculant.

The so produced titanium-silicon slurry was then applied to the floor ofthe cavity in the boron nitride base evaporation vessel (i.e., to itsevaporation surface) and bonded thereto by heating the coated vessel invacuum to a temperature of 1,450 C. in about 4 hours. A hold time ofabout 5 minutes was employed at this temperature. The boron nitride basevessel having its evaporation surface coated with a titanium-siliconalloy was then cooled to room temperature and removed from the furnace.A metallographic examination of the interface zone between the coatingand the boron nitride base vessel showed that the floor of the vesselwas coated with a thin layer of a titanium-silicon alloy which wasmetallurgically bonded thereto by a reaction product formed by reactingthe contacted boron nitride with some of the titanium-silicon alloy.

The vessel of the preceding example was then used as an aluminumevaporation vessel in a conventional evaporation apparatus. The rate ofevaporation of aluminum therefrom was double the rate of aluminumevaporation from a similar but uncoated vessel for the same power inputto the system. This increase in evaporation rate was due to the factthat the aluminum readily and completely wetted the evaporation surfaceof the titanium-silicon coated boron nitride base vessel while such wasnot the case with the uncoated boron nitride base vessel.

The term evaporation as used herein and in the appended claim is meantto describe the surface of the evaporation vessel which is wetted by themetal to be evaporated. It is clear to those skilled in the art thatthis surface generally is the floor of the cavity provided in theevaporation vessel. However, it should be noted that this surface mayalso include the side walls of the evaporation vessel. In addition, itshould be noted that it may not be necessary to coat the entireevaporation surface with a titanium-silicon alloy to realize thebenefits of the instant invention. Accordingly, the instant invention ismeant to include boron nitride base evaporation vessels wherein thewhole as well as a portion of the evaporation surface thereof is coatedwith a titanium-silicon alloy.

From the foregoing, it will be readily appreciated by those skilled inthe art that vessels produced according to the instant invention are notonly ideally suited for use as evaporation vessels for aluminum in aconventional metallizing apparatus, but that they may also find utilityas vessels for molten aluminum and other metals in other metal handlingprocesses.

Accordingly, the example presented herein is for illustrative purposesonly and is not intended to unduly limit the reasonable scope of theinstant invention. The limitations of the invention are set forth in thefollowing claims.

What is claimed is:

l. A vessel comprising from at least 20 to weight per cent boron nitridewith the remainder being a refractory material, and having at least aportion of its surface coated with a titanium-silicon alloymetallurgically bonded thereto.

2. The vessel of claim 1 wherein said refractory material is selectedfrom the group consisting of titanium diboride, zirconium diboride,aluminum nitride, titanium nitride, calcium fluoride and mixturesthereof.

3. The vessel of claim 1 wherein said titanium-silicon alloy comprisesfrom 40 to 80 weight percent silicon with the remainder beingessentially titanium.

4. The vessel of claim 2 wherein said titanium-silicon alloy comprisesfrom 40 to 80 weight per cent silicon with the remainder beingessentially titanium.

5. The vessel of claim 1 for use in the vacuum evaporation of aluminumbase metals, said vessel having an evaporation surface of which at leasta portion is coated with a titanium-silicon alloy metallurgically bondedthereto so as to provide a coated surface which is readily wetted by thealuminum base metals.

6. The vessel of claim 5 wherein said refractory material is selectedfrom the group consisting of titanium diboride, zirconium diboride,aluminum nitride, titanium nitride, calcium fluoride and mixturesthereof.

7. The vessel of claim 5 wherein said titanium-silicon alloy comprisesfrom 40 to 80 weight per cent silicon with the remainder beingessentially titanium.

8. The vessel of claim 6 wherein said titanium-silicon alloy comprisesfrom 40 to 80 weight per cent silicon with the remainder beingessentially titanium.

9. The vessel of claim 5 wherein said vessel comprises 50 weight percent boron nitride with the remainder being essentially titaniumdiboride; and wherein said evaporation surface is coated with atitanium-silicon alloy consisting of 44 weight per cent titanium and 56weight per cent silicon. 1

10. The vessel of claim 5 wherein said vessel comprises a rectangularconfiguration having a cavity therein in which at least one surfacedefining said cavity is the evaporation surface and wherein at least aportion of said evaporation surface is coated with a titanium-siliconalloy metallurgically bonded thereto so as to provide a coated surfacewhich is readily wetted by the aluminum base metals.

* i i i

2. The vessel of claim 1 wherein said refractory maTerial is selectedfrom the group consisting of titanium diboride, zirconium diboride,aluminum nitride, titanium nitride, calcium fluoride and mixturesthereof.
 3. The vessel of claim 1 wherein said titanium-silicon alloycomprises from 40 to 80 weight per cent silicon with the remainder beingessentially titanium.
 4. The vessel of claim 2 wherein saidtitanium-silicon alloy comprises from 40 to 80 weight per cent siliconwith the remainder being essentially titanium.
 5. The vessel of claim 1for use in the vacuum evaporation of aluminum base metals, said vesselhaving an evaporation surface of which at least a portion is coated witha titanium-silicon alloy metallurgically bonded thereto so as to providea coated surface which is readily wetted by the aluminum base metals. 6.The vessel of claim 5 wherein said refractory material is selected fromthe group consisting of titanium diboride, zirconium diboride, aluminumnitride, titanium nitride, calcium fluoride and mixtures thereof.
 7. Thevessel of claim 5 wherein said titanium-silicon alloy comprises from 40to 80 weight per cent silicon with the remainder being essentiallytitanium.
 8. The vessel of claim 6 wherein said titanium-silicon alloycomprises from 40 to 80 weight per cent silicon with the remainder beingessentially titanium.
 9. The vessel of claim 5 wherein said vesselcomprises 50 weight per cent boron nitride with the remainder beingessentially titanium diboride; and wherein said evaporation surface iscoated with a titanium-silicon alloy consisting of 44 weight per centtitanium and 56 weight per cent silicon.
 10. The vessel of claim 5wherein said vessel comprises a rectangular configuration having acavity therein in which at least one surface defining said cavity is theevaporation surface and wherein at least a portion of said evaporationsurface is coated with a titanium-silicon alloy metallurgically bondedthereto so as to provide a coated surface which is readily wetted by thealuminum base metals.